STUDIES ON THE POTENTIAL ENVIRONMENTAL IMPACT OF THE HERBICIDE THIOBENCARB BOLERO

C H Schaefer, T Miura, R J Stewart, and E F Dupras Jr

Mosquito Control Research Laboratory University of California 5544 Air Terminal Drive Fresno CA 93727

In laboratory tests the LC50 of thiobencarb to mosquito fish were ca 3 ppm in static tests and 13 ppm under continuous flow through exposures. In residue accumulation tests blue gill sunfish concentrate thiobencarb into their tissues from water up to levels of 200X within 24 hours but these residues decline with longer exposures. Rinsing of treated fish with untreated water results in a rapid loss of the active ingredient. In static accumulation tests, thiobencarb degraded in soil treated at the suggested user rate and there was no uptake by channel catfish. Field applications of 4 lb AI/acre of both EC and granular formulations resulted in maximum initial water residue levels of ca 1 ppm. This caused some mortality (maximum 25 of mosquito fish) but not enough to indicate a serious problem. Since such applications are only made during the early growing season, the side effects were regarded as minor. It would be best for mosquito abatement districts to stock mosquito fish on rice fields treated with thiobencarb several days after the herbicide application if possible.